WI Nelson Mandela hadn't been around to become the ANC's most prominent spokesman and cause celebre during the 1960s thru to 1990 ? Could the apartheid system have still been challenged and dismantled without his influence ?
I would think so. The underlying structure that apartheid gives the state a moral and of course an economical disadvantage isn´t changed.
Nor is the demographical aspect changed, that more and more black people live there from decade to decade.
But the impact would have been on the "world opinion", I think.
Maybe the anti-apartheit movement doesn´t get fashionable in the West, no movies, etc displaying apartheid slows down the process.
This is a rather interesting scenario. Certainly there would still be resistance to Apartheid. But as it was pointed out, there wouldn't be as strong of a worldwide sentiment. Additionally it is reasonable to believe that the ANC would be even more fractured and violent. If Apartheid can hang on for 11 years longer then the ANC is classified by the Bush administration as being "just another terrorist cell". Even if Apartheid collapses, South Africa has no "Great Leader" who can rise up to be the clear choice to lead his nation.
If you're feeling like a pessimist, no mandela means that the transition away from apartheid turns into a violent revolution full of racial violence...